The present invention relates to an AC motor apparatus and more particularly, an AC motor apparatus which can provide the larger number of revolutions than that determined by the number of poles.
The rotational speed of an AC motor is defined by a power source frequency f Hz and the number of poles P of the motor. The synchronous speed n.sub.s, or the number of revolutions, of the AC motor is given by n.sub.s =2f/P (r.p.s.). The number of real revolutions, however, is smaller than the n.sub.s by an amount of slip. When the power source frequency f is given, an AC motor with the maximum number of revolutions may be obtained with P=2. For the further larger number of revolutions, it is necessary to increase the number of revolutions of the motor mechanically. Alternatively, an output with a frequency larger than the commercial frequency (50 Hz or 60 Hz, for example) is produced by a motor generator or a static frequency converter and is applied to the AC motor. For obtaining the number of revolutions between those defined by P=2 and P=4, a mechanical speed increasing means, a mechanical speed decreasing means or a frequency converting means is used because the number of poles of the AC motor is inherently even. As the mechanical speed changing means, a belt type speed changing apparatus and a gear type speed changing apparatus are known but those are disadvantageous in the space occupied, life time, maintenance, noise and the like. As the frequency converting means, a rotary type or a static type frequency converter are known but those requires a larger space and have a high cost to manufacture. Particularly, the rotary type frequency converter needs a mechanical maintenance. For this, it has been desired that an AC motor is developed which can increase the number of revolutions of the motor by means of an electrical means free from the problems of space, maintenance, noise and cost. One of this type AC motors employs two windings for an armature to which rectifying elements are connected in series, respectively, and through which half-wave rectified currents flow. This proposal, however, can not eliminate the Dc components of the currents flowing through the windings. In this respect, it encounters a difficulty when it is reduced into a practical form.